Electrosensitive recording materials

ABSTRACT

An electrosensitive recording material comprising a nonelectrically-conducting support having a substantially uniform matt surface on which has been vapour deposited a coating, devoid of any overcoat, of a metal having the property of volatilising when contacted by an electrically energized stylus, the characteristics of the matt surface and the amount of metal deposited on the support being such that a visible image of good definition is produced upon application to the material of a stylus energized by A.C.

United States Patent 1 1 [111 33 Atherton Jan. 15, 1974 [54]ELECTROSENSITIVE RECORDING 2,808,345 10/1957 Traub 346/135 x MATERIALSFOREIGN PATENTS OR APPLICATIONS [75] Inventor: David Atherton,Colchester, 708,912 5/1954 Great Britain 346/ 135 England 729,753 3/l966Canada 346/135 [73] Ass1gnee: :Igson Limited, Colchester, PrimaryExaminer joseph w. Hartary g Attorney-Cushman, Darby & Cushman [22]Filed: Sept. 22, 1972 7 21 Appl. No.5 291,165 [57] ABSTRACT Anelectrosensitive recording material comprising anon-electrically-conducting support having a substang 346/135 117/201tially uniform matt surface on which has been vapour E d 74 s 74 Qdeposited a coating, devoid of any overcoat, of a metal having theproperty of volatilising when contacted by an electrically energizedstylus, the characteristics of the matt surface and the amount of metal346/74 SC; ll7/201, 227, 213, 60

[5 6] References Cited deposited on the support being such that avisible UNITED STATES PATENTS image of good definition is produced uponapplication 2,433,515 12/1947 Jahoda 117/60 X to the material of astylus energized by AC.

4 W n2 Prentiss 3 V ELECTROSENSITIVE RECORDING MATERIALS This inventionrelates to electrosensitive recording materials for use in recordingdata from an electrically energized recording member, for example forsonar recording, computer output recording, analogue and digitalrecording, facsimile recording and weather map recording.

Such recording materials comprise a support carrying a thin coating ofvapour-deposited metal, for example of aluminium, zinc or cadmium, andin use for recording the material is traversed with respect to, and withthe metal coating in contact with, a moving recording member which isusually a stylus, generally having a diameter of 0.0030.0l inch, butsometimes a rotating helical blade which makes instantaneous pointcontact with different points of the material. When, and only when,current is supplied to the stylus or blade metal is vaporized from theminute zone of the material with which the stylus or blade is in contactto produce a visible image determined by the electrical signals appliedto the stylus or blade. The thickness of the metal coating must be smallsince otherwise it would be necessary to apply an excessive voltage tothe stylus to effect volatilization of the metal and in any event thethickness of metal which can be vapourdeposited is limited. Thethickness of the metal coating must nevertheless be sufficient to maskthe underlying support effectively in those areas from which it has notbeen removed by the stylus. Otherwise no observable image will beobtained.

When, as is preferred for cheapness, the support is of paper it isnecessary to interpose between the paper and the metal coating a thinlayer of resin to prevent the volatilised metal from penetrating intoand being adsorbed by the paper during its application to the paper.Hitherto the resin used for this backing layer has been devoid of anymatting agent and is present on the support as a smooth glossy filmcarrying the metal coating.

Some forms of apparatus in which such recording has a greater surfacearea than a smooth glossy surface having the same perimeter. When themetal coating is vapour deposited on a suitable matt surface, thesurface coating of metal is no longer present as a smooth film and theeffect of the protuberances is apparently to inhibit the spreading ofthe spark caused upon application of a stylus energized by AC. and soensure an image of sharp definition. This may, perhaps, be due to thematt surface effecting a discontinuity in electrical conductivity of themetal coating, forming it into contiguous areas of greater and lesserelectrical conductivity. To achieve this result it is necessary that thecharacteristics of the matt surface having regard to the amount of metaldeposited on the support should be such that the surface area of thesupport is increased sufficiently to ensure that the spark will notspread while nevertheless not so large as to result in inadequatemasking of the support by the metal which has not been volatilised.

The invention accordingly provides an electrosensitive recordingmaterial comprising a non-electricallyconducting support having asubstantially uniform matt surface on which has been vapour deposited acoating, devoid of any overcoat, of a metal having the property ofvolatilising when contacted by an electrically energized stylus, thecharacteristics of the matt surface and the amount of metal deposited onthe support being such that a visible image of good definition isproduced upon application to the material of a stylus energized by AC.

Preferably the metal-receiving surface is a layer of resin containing amatting agent and deposited from solvent solution upon a base support.if desired, the base support may be of some other material from whichthe resin layer is subsequently stripped.

The thickness of the matt resin coating should be that corresponding toa weight of 0.5 l0 grams/sq.metre (g.s.m.) and is preferably 3 g.s.m.The thickness of the materials are used require application to thestylus of A.C.signals, which may range in voltage from 40-850 volts.Recording material with such a smooth backing layer of resin between thesupport and the metal coating is incapable of providing an image of gooddefinition under these conditions, because the spark produced uponenergization of the stylus tends to spread over the recording surface.This effect can be mitigated by providing another layer of resin as anovercoat on top of the metal coating but this expedient has thedisadvantage of increasing the cost of the material.

This invention is based upon our discovery that it is possible toproduce an electrosensitive recording material which will yield imagesof good definition when subjected to the action of a stylus energized byAC. without the necessity of providing a resinous overcoat by applyingthe vapour deposited metal coating to a support having a matt surface.Thus it is possible to use as the support a film forming resin which hasbeen given a matt surface by inclusion in the resin of a matting agentor by pressing the resin when softened, e.g. by heat or solvent, againsta metal drum having a matt surface.

A matt surface exhibits minute protuberances, constituted in the case ofthe presence of a matting agent by individual particles of mattingagent, and therefore vapour-deposited metal surface coating should bethat conventionally used in recording materials of the type in question,and preferably corresponds to a weight of the metal coating of 0.2g.s.m.

Any film forming resin can be used, for example polyvinyl chloride,polyvinyl chloride/polyvinyl acetate copolymer, cellulose acetatebutyrate, cellulose acetate, polyvinyl butyral or nitrocellulose.Aqueous resin emulsions can also be used.

The particle size ofthe matting agent will normally be in the range of0.01 25 microns and it may be present in the matt resin coating in anamount of l 400% of the weight of the resin. The matting agent isnormally incorporated in the resin by milling together the resin, thesolvent, the matting agent and any other desired ingredients and themilling should be carried out until a spread layer of the milled mixturehas a substantially uniform matt surface exhibiting no aggregates ofmatting agent particles. This can be readily determined by a simpletest.

The matting agent is preferably finely divided silica, for example thematerials sold under the Registered Trade Marks GASIL and AEROSIL.Successful results have been obtained with GASIL 200 which has aparticle size of 7.5 microns and with GASIL 23 which has a particle sizeof 1-3 microns. The former may be present in an amount of 2-70 percentand the latter in the amount of 2-5O percent by weight of the resin.

Examples of other suitable matting agents are Polyvinyl Chloride/AcetateCopolymer Calcium silicate and other metallic silicates Polyethylenewaxes Calcium carbonate Zinc Oxide Titanium dioxide Metallic powdersFelspar Mica Clay

Indeed any finely divided solid which does not dissolve in the solventused is suitable for the purpose.

The resin coating may contain plasticizers and will normally include apigment or dye. It may, however, be colourless when the support iscoloured. The base support is preferably paper but it may be of plasticsfilm. The matting agent, and pigment if present, may be thoroughly mixedwith the resin in a ball mill and the mixture applied to the supportfrom solution in a solvent such as methyl ethyl ketone. Alternativelythe resinous layer may be applied to the base support by ca]- enderingor extrusion and it is also possible to incorporate the matting agent inthe resin during manufacture thereof.

The striking effect produced by the inclusion of a matting agent in theresin will be seen from the follow ing. A conventional electrosensitiverecording material having between a paper support and a vapour depositedcoating of aluminium weighing 0.2 g.s.m. an undercoat of smooth andglossy polyvinyl chloride resin weighing 3 g.s.m. yielded an image whichwas hardly visible when subjected to the action of a stylus pulsed with350 volts A.C. at a frequency of ISKHZ. When this material was modifiedby including 15 percent by weight of GASlL 23 in the resin and usedunder the same conditions a strong image of excellent definition wasobtained.

As will be understood the amount of metal deposited on the materialcontrols the voltage at which maximum marking density occurs. Thisvoltage is also affected by the speed of traverse of the material.

While the above-described electrosensitive recording material has thespecial advantage that it is capable of yielding a satisfactory imagewhen used with a stylus energized with A.C. it has a further advantageof versatility in that it can also be satisfactorily used with a stylusenergizedby DC. or pulsed D.C., even by DC. voltages less than 1 volt.Moreover, it is cheap to produce, requiring only two coating layers, andit has been found to be less critical of stylus pressure than previouslyavailable materials.

The following are specific examples of materials according to theinvention:

Example 1 parts by weight Methyl Ethyl Ketone (MEK) 90 Carbon BlackGasil 23 After matting, this mixture was coated onto white paper to givea weight of approximately 3 g.s.m. Aluminium was then vapour depositedonto the resinous layer to give acoating weight of 0.25 g.s.m.

When cut at 400 volts A.C. at a frequency of 18 KHz and a stylus topaper speed of 200 in/sec. the material gave a black image with gooddefinition on a white background. This paper also gave a good black markwith voltages of less than 1 volt DC. at slow speed and up to 60 voltsDC. at faster speeds.

Example 2 Cellulose Acetate Butyrate l0 parts by weight Gasil 200 3Carbon Black 1.0 MEK/Toluene 90 i This mixture was coated on paper andmetallised as in Example 1.

Example 3 Cellulose Acetate Butyrate 10 parts by weight Gasil 23 1.5

MEK

This material was coated onto polyester film base to give a coatingweight of l g.s.m. Aluminium was then vapour deposited to give a coatingweight of 0.18 g.s.m. When cut at 250 volts A.C. at a frequency of 29KHz with a paper to stylus speed 50 in/sec the material gave atransparent image. It also gave satisfactory results at low D.C.voltages.

Example 4 Example 5 Paraloid AT/SO parts by weight (Acrylic Resin)Superfine Superl'los l0 MEK 300 lrgalite Red Pigment 5 Coating andvacuum metallisation were as in Example 1. The material gave a red imageon a white background.

Example 6 PVC/Polyvinyl Acetate Copolymer MEK Micronised Red Iron Oxide10 parts by weight 90 Coating and vacuum metallisation were as inExample Example 7 As in Example 6 with 4.0 parts micronised CalciumCarbonate instead of Iron Oxide. The material gave a transparent image.

Example 8 PVC/Polyvinyl Acetate Copolymer 10 parts by weight MEK 90Carbon black 20 Coating and metallisation were as in Example 1.

Example 9 Clear PVC film was softened with MEK and pressed against amatt steel drum. The film was then dried and metallised as in Example 1.

The back of this film can be coated with lacquers of different coloursto' give the desired contrast to the white background.

In the examples, the stylus was energized with AC. at a voltage rangingfrom a low of 250 in example 3 to a high of 400 in example 1.

What I claim as my invention and desire to secure by Letters Patent is:

1. An electrosensitive recording material, capable of use with a stylusenergized with AC. at a voltage of 250-400 volts, comprising a baselayer of nonelectrically conducting material, a coating of film formingresin on said base layer and weighing from 0.5 to grams/square metre,said resin coating having a nonsmooth external surface impervious tovapour deposited metal and containing, in an amount of 2 to 70 percentby weight of the resin, a matting agent having a particle size in thrange of 0.01 to 25 microns, and a layer of vapour deposited metal onthe external surface of said resin coating.

2. A material as claimed in claim 1, wherein the base layer is a sheetof paper.

3. A material as claimed in claim 1, wherein the matting agent is silicaof particle size 1 3 microns and present in an amount of 2 50 percent byweight of the resin.

4. A material as claimed in claim 1, wherein the matting agent is silicaof particle size 7.5 microns and present in an amount of 2 percent byweight of the resin.

2. A material as claimed in claim 1, wherein the base layer is a sheet of paper.
 3. A material as claimed in claim 1, wherein the matting agent is silica of particle size 1 - 3 microns and present in an amount of 2 - 50 percent by weight of the resin.
 4. A material as claimed in claim 1, wherein the matting agent is silica of particle size 7.5 microns and present in an amount of 2 - 70 percent by weight of the resin. 